Last edited March 25, 2011.
Folding Your Hand in Zung Jung by Chris Schumann is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.
Mahjong is typically a long game. 16 hands is typical for Chinese styles, at least 8 hands for modern Japanese. To win the game, you need the highest score at the end. All the modern styles give a significant penalty to the person who throws somebody's big winner, and that can move you from first place to last in a single hand if you're not careful.
In Zung Jung, everyone pays for small hands. Since there's no extra penalty for throwing the winning tile to someone who scores 25 or less, you can continue to build your hand until you think someone is building a big hand. If you see the beginnings of Big Four Winds, Big Three Dragons, Three Consecutive Triplets, or even a hand with one single suit, you have several options. First, you can try to go out quickly on anything at all, but sometimes you are too far away for that. Second, you can try to help someone else (maybe last place) win. That's pretty advanced stuff. Third, you can play safe and fold.
If you've decided that your hand is too far from winning, or that you don't want to risk throwing that winning tile, that's when it's time to fold your hand. Unlike poker, where you can actually quit a hand, in mahjong you have to play along, and every tile you throw can be used against you. Here's how you do it in mahjong.
First, throw tiles that you know cannot be used by your opponent. Any honor tile he's punged is absolutely safe. Not so for suit tiles! If he's going for one suit and has a pung of three dots, the fourth one could be used in a chow to win. Your two bamboo is safe if enough twos and threes are accounted for, keeping in mind that he might just need to finish his pair. Any tile he throws immediately before you is safe. More precisely, the rule of same turn immunity says he can still call your tile for the win, but if he just discarded it, the game is scored as if he drew the tile from the wall, and you will not pay extra. This same rule can save you in the more common case: Any tile just thrown is safe for you to throw. The player to your left throws 7 dots. You throw 7 dots. The player across from you calls mahjong. The player to your left pays for throwing that tile. Any calls of discards interrupt this immunity.
Next, throw tiles that might be safe. These are tiles most recently discarded by him, then tiles most recently discarded by others, then tiles discarded by him earlier, then those discarded earlier by others. Keep in mind the Thirteen Terminals hand: Your single red dragon might not be safe to throw even if it's the fourth one to be played if your opponent has a concealed hand with very few honors and terminals in his discards. What if you must throw a new discard? Consider your opponents most recent discard. This is the tile that has been held until near the end, so it's possible he has tiles that are close to it, but those close tiles could be safe, or they could be dangerous. More tiles that might be safe are your concealed sets. You've got a set of green dragons? Throw them away. Your own wind? Sorry, everything must go.
Your least-best option if you have nothing that's safe, is to throw something that you think could help someone with a smaller hand. Three Similar Sequences is much cheaper to pay than Three Consecutive- or Similar- Triplets.